Interfacial Strain Analysis of Bending Bilayer Silicone Elastomer Films Using a Cholesteric Liquid Crystal Sensor

The analysis of the bending strain at the interface of layered polymer films is significant in the design of flexible electronic devices because conductive materials placed on the interface are degraded by strain. Although theoretical calculations and numerical simulations of the interfacial bending strain of polymer films have been conducted, few experimental analyses have been reported because of the difficulty in measuring the interface strain. In our previous study, the internal strain in a bending polymer film was successfully measured using a cholesteric liquid crystal elastomer (CLCE) sensor. Herein, we report the interfacial strain analysis of a bending bilayer film composed of poly(dimethylsiloxane) (PDMS) films with different Young's moduli using a CLCE sensor. The experimental strain analysis revealed that the bending strain at the interface depends on the distance between the interface and the neutral mechanical plane (NMP), which experiences no strain. Notably, as the bilayer films bend significantly, the NMP shifts toward the inner bending surface because of the change in the balance between the tensile and compressive stresses in the film. This study enables us to understand the interface bending strain in polymer films, which will aid in the design of flexible electronic devices with conductive materials placed on the interface whose strain is minimized.